1. Field of the Invention
The present invention relates to a lifting jack with safety and release system, particularly to a lifting jack with safety and release system for safe and convenient lowering of a lifted object.
2. Description of Related Art
A conventional hydraulic lifting jack has no safety system, due to restricted space and for simplicity. When the hydraulic cylinder breaks or leaks, the lifted object will suddenly or at least slowly come down unnoticed, posing a danger for the unaware user.
Therefore U.S. Pat. No. 5,618,029 discloses a lifting jack safety system, wherein a safety pawl is attached to the support arm or link arm on the top of the lifting jack, engaging with an asymmetrically saw-toothed ratchet. When the lifting jack is raised, the pawl glides over the teeth of the ratchets. At the same time, it is blocked from moving back, preventing the lifting jack from lowering. To lower the lifting jack intentionally, the pawl is turned away and thus no longer blocked by the ratchet. This safety system prevents unwanted lowering of the lifting jack. However, when the lifting jack is lowered, the pawl has to be constantly kept away from the ratchet, which makes it uncomfortable to use.